1. Field of the Invention
The present invention relates generally to magnetically levitated (maglev) pumps and controlling circuits, and more specifically to clean pumps employing a magnetic bearing, such as maglev pumps for use in artificial hearts and other similar medical equipment, and controlling circuits.
2. Description of the Background Art
FIGS. 16A and 16B show a conventional maglev pump. More specifically, FIG. 16A is a vertical cross section thereof and FIG. 16B is a cross section thereof taken along a line XVIBxe2x80x94XVIB.
A shown in FIG. 16A, the maglev pump 1 is configured by a motor unit 10, a pump unit 20 and a magnetic bearing unit 30. In pump unit 20 internal to a casing 21 a pump chamber 22 is provided and therein an impeller 23 rotates. As shown in FIG. 16B, impeller 23 has a plurality of vanes 27 formed spirally.
Casing 21 is formed of a non-magnetic member and impeller 23 includes a non-magnetic member 25 having a permanent magnet 24 constituting a non-controlled magnetic bearing, and a soft magnetic member 26 corresponding to a rotor of a controlled magnetic bearing. Permanent magnet 24 is divided in a direction of a circumference of impeller 23 and adjacent magnets are magnetized to have opposite magnetic poles. Opposite to that side of impeller 23 having permanent magnet 24, a rotor 12 is provided external to pump chamber 22, supported by a bearing 17.
Rotor 12 is driven by a motor 13 to rotate. Rotor 12 is provided with the same number of permanent magnets 14 as permanent magnets 24 of impeller 23 to face permanent magnets 24 and also create attractive force. Adjacent permanent magnets 14 are also magnetized to have opposite magnetic poles.
Opposite that side of impeller 23 having soft magnetic member 26, at least three electromagnets 31 and at least three positional sensors 32 are provided circumferentially in magnetic bearing unit 30 to attain balance with the attractive force of permanent magnets 24 and 14 in pump chamber 22 to maintain impeller 23 at a center of casing 21. Electromagnet 31 has a geometry of the letter C and position sensor 32 is a magnetic sensor.
In maglev pump 1 thus configured an attractive force acts axially between permanent 14 buried in rotor 12 and permanent magnet 24 provided to impeller 23. This attractive force contributes to magnetic-coupling, which rotatably drives impeller 23 and also provides radial supporting stiffness. To achieve balance with the attractive force, C-shaped electromagnet 31 has a coil passing electric current to levitate impeller 23.
When rotor 12 is rotated by a driving force provided by motor 13 formed by motor rotor 15 and motor stator 16, permanent magnets 14 and 24 form magnetic-coupling and impeller 23 thus rotates to suck a fluid through a suction port 60 and discharge the fluid through an outlet 70. Since impeller 23 is isolated from rotor 12 by casing 21 and is also not contaminated by electromagnet 31, maglev pump 1 discharges a fluid (blood if the pump is used for blood pump) maintained clean.
FIG. 17 shows the FIGS. 16A and 16B maglev pump and a circuit controlling the same. In FIG. 17, a maglev pump 200 is shown in a perspective view, at seen at a suction port 60 shown in FIG. 16A, and an axis of rotation of impeller 23 is surrounded by three electromagnets M1-M3 and three sensors S1-S3. Sensors S1-S3 provides their respective outputs which are inputs to sensor amplifiers H1-H3, respectively, amplified thereby and thus output to an operation circuit 202.
Operation circuit 202 performs an operation on sensor outputs amplified by sensor amplifiers H1-H3 and outputs to a phase compensation circuit 203 a voltage a proportional to a gap between electromagnet M1 and impeller 23, a voltage b proportional to a gap between electromagnet M2 and impeller 23, and a voltage c proportional to a gap between electromagnet M3 and impeller 23.
Phase compensation circuit 203 includes proportional plus derivative circuits PD1-PD3 and integral circuits I1-I3. Proportional plus derivative circuit PD1 and integral circuit I1 receive control voltage a. Proportional plus derivative circuit PD2 and integral circuit I2 receive control voltage b. Proportional plus derivative circuit PD3 and integral circuit I3 receive control voltage c. An output of proportional plus derivative circuit PD1 and that of integral circuit I1 are added together and thus output to a limit circuit LM1. An output of proportional and derivative circuit PD2 and that of integral circuit I2 are added together and thus output to a limit circuit LM2. An output of proportional plus derivative circuit PD3 and that of integral circuit I3 are added together and thus output to a limit circuit LM3. If limit circuits LM1-LM3 receive a signal of positive voltage they pass the signal and if they receive a signal of negative voltage then they compulsorily set the signal to be 0V. Limit circuits LM1-LM3 have their respective output signals input to power amplifiers A1-A3, respectively. Power amplifiers A1-A3 amplify the output signals, respectively, to drive their respective electromagnets M1-M3. Thus the control circuits allow an operation to be performed based on the outputs of sensors S1-S3 individually for electromagnets M1-M3 to drive electromagnets M1-M3.
FIG. 18 is a block diagram showing another example of the circuit controlling the maglev pump. The FIG. 17 control circuit includes phase compensation circuit 203 having proportional plus derivative circuits PD1-PD3 and integral circuits I1-I3 independently provided for electromagnets M1-M3, whereas the FIG. 18 control circuit, does not have an independent phase compensation circuit for each electromagnet. More specifically, it is provided with a phase compensation circuit for each mode of movement of an impeller controlled by a magnetic bearing. Herein, impeller 23 has separate modes of movement including a translative movement in the direction of an axis of translative movement of the impeller, and rotative movements around the axis of translative movement of the impeller, orthogonal to each other relative to the axis, i.e., a pitching movement and a yawing movement.
With reference to FIG. 18, separation circuit 204 performs an operation on sensor signals output from sensor amplifiers H1-H3 and outputs the impeller 23 translative movement parameter z, pitching movement parameter xcex8x and yawing movement parameter xcex8y. Phase compensation circuit 205, as well as the FIG. 17 phase compensation circuit 203, considers each mode of movement and it is configured by proportional plus derivative circuits PD1-PD3 and integral circuits I1-I3 providing their respective outputs which are fed through a distributor 206 for distribution to electromagnets M1-M3 to pass electric current to electromagnets M1-M3 via limit circuits LM1-LM3 and power amplifiers A1-A3.
If the FIG. 16A maglev pumps 1 is used as a mobile pump or it is buried in a human body in the form of a blood pump, the entirety of the pump would move while impeller 23 rotates. Furthermore, the FIG. 16A impeller 23 in the form of a disc pitches and yaws as it rotates, and the entirety of the pump is thus affected by gyroscopic moment, disadvantageously resulting in precession, swaying around.
If impeller 23 is rotating and pitching and yawing movements are applied to the pump, a gyroscopic moment proportional to the movements"" speed acts on impeller 23. This gyroscopic moment results in impeller 23 being affected by a gyroscopic moment having an axis of rotation orthogonal to a rotative movement, such as pitching, applied to the pump as disturbance and impeller 23 thus displaces in pump chamber 22, and triggered thereby is a precession of a low frequency in the direction opposite to the direction in which impeller 23 rotates.
In particular, if the pump is used as a blood pump and the precession results in casing 21 and impeller 23 contacting with each other, thrombus readily forms there. Thus, desirably the precession should be minimized. The precession may be reduced by increasing the size of the electromagnet to enhance the stiffness of the magnetic bearing, although such cannot be adopted if the pump is used as a blood pump implanted in a body as it is required to be minimized.
Therefore the present invention mainly contemplates a maglev pump and a circuit controlling the same without requiring the pump to be increased in size, capable of steadily supporting a rotating impeller by compensating for a gyroscopic moment introduced in response to a disturbance applied to the pump when the pump is used in the form of a mobile pump.
The present invention provides a maglev pump including: an impeller in the from of a disc magnetically levitated and thus rotated for delivery of fluid, the impeller having one surface provided with a first ferromagnetic body and the other surface circumferentially provided with a second ferromagnetic body; an electromagnet closer to one side of the impeller to face the first ferromagnetic body to attract the impeller toward one side; a permanent magnet arranged closer to the other side of the impeller circumferentially to face the second ferromagnetic body; and a mechanism arranged closer to one side of the impeller to transmit to the impeller without contacting the impeller a force driving and thus rotating the impeller, wherein the impeller is magnetically levitated by controlling an electric current flowing through the electromagnet to provide in balance an attractive force provided by the electromagnet and applied to the second ferromagnetic body, an attractive force provided by the electromagnet and applied to the first ferromagnetic body, and a force generated by the mechanism to act on the impeller in the direction of an axis of rotation.
Since an electromagnet of a magnetic bearing can be arranged closer to the mechanism transmitting a force driving and thus rotating the impeller, the pump can be reduced in length in the axial direction and thus miniaturized. Furthermore, a permanent magnet serving to additionally provide a passive magnetic bearing can enhance the stiffness of the impeller in the radical direction.
Preferably, the impeller has one side circumferentially provided with a first electromagnet, and the mechanism includes a rotor having the other surface circumferentially provided with a second permanent magnet opposite the first permanent magnet, and having one surface serving as a motor rotor, and a motor stator provided opposite one side of the motor rotor.
Arranging the electromagnet closer to the motor can reduce the length of the magnetic bearing unit in the axial direction.
More preferably, the ferromagnetic body is arranged closer to an inner diameter of the impeller opposite the electromagnet and the first permanent magnet is arranged closer to an outer diameter of the impeller circumferentially, and the electromagnet is arranged closer to an inner diameter and the motor rotor is arranged closer to an outer diameter.
More preferably, the first permanent magnet is arranged closer to an inner diameter of the impeller circumferentially and the first ferromagnetic body is arranged closer to an outer diameter of the impeller opposite the electromagnet, and the motor rotor is arranged closer to an inner diameter and the electromagnet is arranged closer to an outer diameter.
Arranging the electromagnet closer to the outer diameter allows the electromagnet to have an increased winding space.
More preferably the mechanism includes a motor rotor arranged closer to one side of the impeller and a motor stator arranged opposite the motor rotor.
Thus a motor and a motor bearing supporting the rotor can be dispensed with.
The present invention in another aspect provides a control circuit controlling a magnetically levitated pump, applying an electromagnetic attractive force in one direction of an impeller and at least one of a magnetic attractive force to support the impeller without contacting the impeller, the control circuit having a sensor detecting a position of the impeller and an electromagnet applying the electromagnetic attractive force to the impeller to position the impeller, including: a separation circuit driven by an output of the sensor to separate a movement of the impeller into a translative movement in a direction of an axis of rotation of the impeller, a pitching movement and a yawing movement; a phase compensation circuit including a proportional-plus-derivative circuit and one of an integral circuit and a lowpass circuit in parallel with the proportional-plus-derivative circuit for each movement provided by the separation circuit; and a limit circuit connected to the phase compensation circuit at one of an input and an output of one of the integral circuit and the lowpass circuit controlling the translative movement.
Preferably, when the integral circuit controlling the translative movement outputs a signal indicating that the impeller leans closer to the electromagnet than a position set for the impeller to be levitated, the limit circuit disconnects one of the input and the output of one of the integral circuit and the lowpass circuit.
Preferably, the limit circuit limits the output of the integral circuit controlling the translative movement, to a signal of one of positive and negative outputs of one of the input and the output of one of the integral circuit and the lowpass circuit.
The present invention in still another aspect provides a control circuit controlling a magnetically levitated pump, applying an electromagnetic attractive force in one direction of an impeller and at least one of a magnetic attractive force to support the impeller without contacting the impeller, the control circuit having a sensor detecting a position of the impeller and an electromagnet applying the electromagnetic attractive force to the impeller to position the impeller, including: an operation circuit operative in response to an output of the sensor to perform an operation to calculate a distance between the electromagnet and the impeller; a phase compensation circuit including in parallel a proportional plus derivative circuit and one of an integral circuit and a lowpass circuit receiving a signal output from the operation circuit; and a limit circuit connected to one of an input and an output of one of the integral circuit and the lowpass circuit.
Preferably, when the integral circuit controlling the translative movement outputs a signal indicating that the impeller leans closer to the electromagnet than a position set for the impeller to be levitated, the limit circuit disconnects one of the input and the output of one of the integral circuit and the lowpass circuit.
Preferably, the limit circuit limits the output of the integral circuit controlling the translative movement, to a signal of one of positive and negative outputs of one of the input and the output of one of the integral circuit and the lowpass circuit.
More preferably the maglev pump is used for blood circulation.
The present invention in still another aspect provides a control circuit controlling a magnetically levitated pump, applying an electromagnetic attractive force in one direction of an impeller and at least one of a magnetic attractive force to support the impeller without contacting the impeller, the control circuit having a sensor detecting a position of the impeller and an electromagnet applying the electromagnetic attractive force to the impeller to position the impeller, including: a separation circuit driven by an output of the sensor to separate a movement of the impeller into a translative movement in a direction of an axis of rotation of the impeller, a pitching movement and a yawing movement; a phase compensation circuit applying proportional, derivative and integral elements for each of the translative, pitching and yawing movements to control an electromagnetic attractive force of the electromagnet; and a filter circuit extracting only a low frequency component from each movement parameter for addition to an input of the phase compensation circuit controlling the pitching and yawing movements, wherein compensation is made for a gyroscopic moment introduced when the impeller is rotating.
The present invention in still another aspect provides a control circuit controlling a magnetically levitated pump, applying an electromagnetic attractive force in one direction of an impeller and at least one of a magnetic attractive force to support the impeller without contacting the impeller, the control circuit having a plurality of sensors detecting a position of the impeller and a plurality of electromagnets applying the electromagnetic attractive force to the impeller to position the impeller, including: an operation circuit operative in response to an output of the sensor to perform an operation to calculate a distance between the electromagnet and the impeller; a phase compensation circuit controlling an electromagnetic attractive force of each of the electromagnets via proportional, derivative and integral elements receiving a signal output from the operation circuit; and a filter circuit extracting a low frequency component from a signal obtained from an operation calculating a distance between an adjacent one of the electromagnets and the impeller, wherein an output of the filter circuit is added to compensate for a gyroscopic moment introduced when the impeller is rotating.
Furthermore, the present invention in another aspect provides a control circuit controlling a magnetically levitated pump, applying an electromagnetic attractive force in one direction of an impeller and at least one of a magnetic attractive force to support the impeller without contacting the impeller, the control circuit having a plurality of sensors detecting a position of the impeller and a plurality of electromagnets applying the electromagnetic attractive force to the impeller to position the impeller, including: an operation circuit operative in response to an output of the sensor to perform an operation to calculate a distance between the electromagnet and the impeller; a phase compensation circuit controlling an electromagnetic attractive force of each of the electromagnets via proportional, derivative and integral elements receiving a signal output from the operation circuit; and an addition circuit adding only a signal output from a corresponding the integral element and an output of an adjacent the phase compensation circuit together, wherein compensation is made for a gyroscopic moment introduced when the impeller is rotating.
Thus in the present invention if the pump is used in the form of a mobile pump, compensation can be made for a gyroscopic moment introduced in response to a rotative disturbance applied to the pump, and the impeller can thus be supported steadily as it rotates.
Still more preferably the pump includes a circuit detecting a rotation speed of the impeller to alter a level of compensation for the gyroscopic moment.
Still more preferably the maglev pump is used for blood circulation.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.